Asymmetric data path media access controller

ABSTRACT

A method and apparatus for maintaining data throughput in a data element includes receiving a clock and a first plurality of instances of data having a first width on an input, sampling consecutive ones of instances of the data having the first width at consecutive ones of a first rising edge and a first falling edge of the clock, respectively, to generate two plurality of instances of sampled data having a first width. The plurality of instances of sampled data is then sampled at a second rising edge of the clock and parallelized to generate a second plurality of instances of parallel data having a second width greater than the first width. The parallel data may then be processed to for example generate statistics to monitor link integrity, prior to being transmitted. A 10 Gbps data transmission speed may be maintained using the IEEE 802.3ae-specified media independent interface clock.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent applicationSer. No. 60/234,396, inventor Michael Tate, entitled ASYMMETRIC DATAPATH MEDIA ACCESS CONTROLLER filed on Sep. 21, 2000, the contents ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for maintainingthroughput in a data element, and more particularly, to a method andapparatus for maintaining throughput in a data element by using asampling scheme to increase the number of bits at an output as comparedwith an input.

BACKGROUND

The Institute of Electrical and Electronics Engineers (IEEE) Standard802.3ae, entitled “Ten Gigabit Per Second Ethernet Task Force” defines agigabit per second industry standard for interconnectinghigh-performance switches, routers, servers, and the like in thebackbone of local area networks (LANs), Metropolitan Area Networks(MANs), native attachments to a Wide Area Network (WAN), and the like.Two features specified by the 802.3ae standard are a 32-bit data pathand a clock. In operation, the 32-bit data and clock are received by aphysical layer device and forwarded through a Media IndependentInterface (MII) to a Media Access Controller (MAC).

The MAC resides on the data path between the Physical Layer Controller(PHY) and a Packet Switching Controller (PSC). In accordance withindustry standards a MAC is required to support certain standardizedfeatures and functions. However, MAC designers often have flexibility,to determine how to support the standardized functions and features.

Data transmission speed across the data path is generally a product ofthe data path width and the data sampling speed. In addition, the clockfrequency of a data transmission system is inversely proportional to thedata path width if the same total aggregate throughput is to bemaintained in a pipelined system. It is known to implement Ethernet MAClayer logic as a pair of same bit width receive and transmit data pathsto which operations are performed. As such, it then follows that thesame size receive and transmit data paths in a MAC application willrequire the same clock frequencies for each path.

For the transmit data path, the desired clock frequency is easilygenerated by an external commercial oscillator. For the receive datapath, however, the receive clock is derived from the IEEE specified MIIreceive data clock. The specified MII-supplied clock frequency, however,is inadequate to maintain certain data rates such as, for example, a 10Gbps data transmission rate, using rising edge only sampling of 32-bitwide data. In fact, the MII-supplied receive clock specified by the IEEEstandard is approximately half the frequency required to generate the 32bit data path as desirable at a 10 Gbps data rate on the transmit side.

The deficiencies of present methods for maintaining data throughput athigh data rates show that a need exists for maintaining high datathroughput in a data element compatible with standardized featuresspecified by IEEE 802.3ae.

SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention provides an asymmetricdata path for achieving a high data throughput such as, for example 10Gbps or greater. In accordance with an exemplary embodiment the desiredclock frequency for a transmit data path, may be generated by anexternal commercial oscillator. However, the receive clock is derivedfrom a standardized clock having a frequency that would otherwise be tooslow using conventional methods to support the data throughput rate.Therefore, an exemplary embodiment of the present invention includes anasymmetric data path wherein the width of the receive data path isgreater than that of the transmit data path to accommodate the differentclock rates for the receive and transmit data paths.

Accordingly, an exemplary method for maintaining throughput in a datapath includes the steps of receiving a clock and a plurality ofinstances of data having a first width on an input, processingconsecutive ones of the plurality of instances of data having the firstwidth to produce more than one of a plurality of instances of datahaving a second width wherein the second data width are equivalent tothe first data width and the more than one of the plurality of instancesof data having the second data width are used to produce a plurality ofinstances of data having a third data width wherein the third data widthare greater than the second data width and the plurality of instances ofdata having the third data width are used to produce a plurality ofinstances of data having an output data width wherein the output datawidth are equivalent to the third data width, and transmitting theplurality of instances of data having the output data width.

The invention provides a method for maintaining throughput in a dataelement, such as, for example, a 10 Gigabit Ethernet MAC receivefunction element, without introducing unnecessary risk and complexityassociated with using multiplied clock sampling or rising and fallingedge sampling throughout the receive function element. In anotherembodiment of the present invention, the method includes the steps ofreceiving at a first element a clock and a first plurality of instancesof data having a first bit-width as an input, transmitting the clock andfirst plurality of instances of data having the first width to a secondelement, operating on the first plurality of instances of data havingthe first width to produce a second plurality of instances of datahaving a second width, transmitting the clock and second plurality ofinstances of data having the second width to a third element, operatingon the second plurality of instances of data having the second width toproduce a third plurality of instances of data having a third width,transmitting the third plurality of instances of data having the thirdwidth to a fourth element, and operating on the third plurality ofinstances of data having the third width to produce a fourth pluralityof instances of data having a fourth width.

In another embodiment of the present invention, the method includes thesteps of receiving a first data having first bit-width bits, managementbits and clock bits, inputting the first bit-width bits and clock bitsinto a receive data path, and processing the first bit-width bits togenerate processed data having a second bit-width which is greater thansaid first bit-width.

In another embodiment of the present invention, the switch includes oneor more ports for receiving a plurality of inbound packets and fortransmitting a plurality of outbound packets, a physical layer devicecoupled to the input ports for receiving the plurality of inboundpackets, a media independent interface coupled to the physical layerdevice for receiving the plurality of inbound packets from the physicallayer device, a media access controller coupled to the media independentinterface for receiving the output of the media independent interfaceand for processing the output of the media independent interface toincrease bit width, and a packet switching controller coupled to themedia access controller for receiving the increased bit width data andfor transmitting the increased bit width data.

In another embodiment of the present invention, the media accesscontroller includes a first gate for sampling an input data streamhaving a first bit width in accordance with a first rising edge of aclock, a second gate for sampling said input data stream in accordancewith a first falling edge of a clock, and a third gate coupled to saidfirst and second gates for combining outputs of said first and secondgates in accordance with a second rising edge of said clock to producean output data stream having a second bit width greater than said firstbit width.

In yet another embodiment of the present invention, the media accesscontroller includes a first data path having a first bit-width, and asecond data path including a receive function element that receivesinput data at said first bit width and processes said input data togenerate output data having a second bit width greater than said firstbit width.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a simplified block diagram of a system having a media accesscontroller for providing bi-directional communication between a packetswitch and one or more local area networks;

FIG. 2 is a simplified block diagram of the media access controller ofFIG. 1 in accordance with an exemplary embodiment of the presentinvention;

FIG. 3 is a block diagram illustrating greater details of the system forproviding bi-directional communication between a packet switch and oneor more local area networks illustrated in FIG. 1 in accordance with anexemplary embodiment of the present invention;

FIG. 4 is a simplified block diagram of the receive function element ofthe system of FIG. 3, in accordance with an exemplary embodiment of thepresent invention;

FIG. 5 is a wave diagram of the clock signal that graphicallyillustrates data sampling in accordance with an exemplary embodiment ofthe present invention;

FIG. 6 graphically illustrates the timing of receive function of FIG. 4in accordance with an exemplary embodiment of the present invention; and

FIG. 7 is a flow chart showing a method for processing the data inaccordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An exemplary embodiment of the present invention provides an asymmetricdata path for achieving a high data throughput such as, for example 10Gbps, using a standardized clock having a frequency that would otherwisebe too slow using conventional methods to support the data throughputrate. In order to appreciate the advantages of the present invention, itwill be beneficial to describe the invention in the context of anexemplary network system, such as for example a high speed Ethernetswitch. One of skill in the art will appreciate that the presentinvention is not limited to the described exemplary embodiment. Rather,the present invention may be utilized to provide a higher throughputdata rate in any symmetric or asymmetric data path.

FIG. 1 is a simplified block diagram illustrating an exemplary operatingenvironment of the present invention. In accordance with an exemplaryembodiment, a switch 100, comprising one or more media independentinterfaces (MII) 114(a) and 114(b), one or more PHYs 108(a) and 108(b)and one or more MACs 104(a) and 104(b) provides bi-directionalcommunication between a packet switching controller (PSC) 102 anddevices, such as, for example a personal computer (PC) or Ethernet phoneoperating on LANs 112(a) and 112(b).

The media independent interfaces 114(a) and 114(b) provide abidirectional interface between the PHYs 108(a) and 108(b) and the MACs104(a) and 104(b) respectively. The PHYs 108(a) and 108(b) preferablyreceive inbound packets and transmit outbound packets to the LANs 112(a)and 112(b) respectively. The PHYs preferably perform flow independentphysical layer operations on the inbound packets. In accordance with anexemplary embodiment, the PHYs may perform all the physical layerinterface (PHY) functions for full duplex or half-duplex Ethernet.

For example, in the described exemplary embodiment the PHYs may decodereceived data packets and encode output data packets in accordance witha variety of standards such as for example 4B5b, MLT3, and Manchesterdecoding. The PHYs 108(a) and 108(b) may also perform clock and datarecovery, stream cipher de-scrambling, and digital adaptiveequalization.

In the described exemplary embodiment, MACs 104(a) and 104(b) performflow independent MAC layer operations on the inbound packets. Forexample, MACs 104(a) and 104(b) may process the received Ethernetpackets and forward higher layer packets to the PSC 102. The PSC 102preferably receives the inbound packets, classifies the packets,generates application data for the inbound packets, modifies the inboundpackets in accordance with the application data, and transmits themodified inbound packets onto, for example, a switching backplane.

In an exemplary embodiment the packet switching controller 102 may alsoreceive outbound packets from other packet switching controllers overthe backplane. The PSC 102 may then transmit the outbound packets to theMACs 104(a) and 104(b) for forwarding to local devices via the MIIs114(a) and 114(b), PHYs 108(a) and 108(b) and LANs 112(a) and 112(b),respectively. In an exemplary embodiment of the present invention, theMACs 104(a) and 104(b) encode packets in the transmit path into Ethernetpackets for communication to external device operating on the local areanetwork. The MACs 104(a) and 104(b) may also perform additionalmanagement functions such as, for example, link integrity monitoring.

In other embodiments, the packet switching controller 102 may subjectone or more outbound packets to egress processing prior to forwardingthem to the MACs 104(a) and 104(b). Further, the packet switchingcontroller 102 may be implemented in non-programmable logic,programmable logic or any combination of programmable andnon-programmable logic.

Referring to FIG. 2, an exemplary MAC 104, in accordance with thepresent invention, comprises a transmit function element 300, andtransmit control element 120 coupled between a management controlelement (MCE) 101 and PSC 102 in the transmit path. In the describedexemplary embodiment the transmit control element 120 receives outboundpackets from the PSC 102. An exemplary transmit control element may,upon request by the system, conditionally transmit special packets (flowcontrol packets) that disable and enable packet transmission from theMAC on the other side of the link. In addition, preferably under controlof the receive control element, the transmit control element may alsoprohibit flow of frames from the system to the transmit function element300.

In an exemplary embodiment of the present invention, the transmitfunction element 300 may process outbound packets in accordance with oneor more operative communication protocols, such as, for example, mediaaccess control (MAC) bridging and Internet Protocol (IP) routing. Thetransmit function element 300 may encapsulate outbound data with theappropriate MAC address of the external device on the LAN before sendingover the MII 114.

Further, an exemplary MAC may also comprise a receive function element200 and a receive control element 130 coupled between the MCE 101 andthe PSC 102. An exemplary receive function element 200 receives inboundpackets from the MCE 101 and preferably removes the data from the framesand checks for transmission errors in the received frames. In anexemplary embodiment the receive control element recognizes specialpackets (e.g. flow control packets) that disable and enable packettransmission from the MAC to the PSC 102.

FIG. 3 is a simplified block diagram illustrating the exemplary datapath of FIG. 2 in greater detail. An exemplary system may comprise asystem interface 150, and PHY 108. An exemplary MAC 104 may include thetransmit control element 120, the receive control element 130, thetransmit function element 300, the receive function element 200, and amanagement control element (MCE) 101.

In operation, the PHY 108 communicates incoming data packets to the MCE101 through a 76 bit data path within the MII 114. In one embodiment anincoming data packet preferably comprises 32 bits of data, 4 bits ofcontrol information, and 2 bits of management information. MCE 101communicates configuration information to, and retrieves statusinformation from ISO Layers below the MAC layer via the managementinformation bits. In the described exemplary embodiment the MCE 101removes the management information, and forwards the remaining 32 databits and the 4 bits of control data to the receive function element 200.

In an exemplary embodiment, the receive function element 200 may providereceive functionality in accordance with a variety of communicationsprotocols, such as, for example, IEEE 802.3ae receive functionality asrelated to the MAC layer. Similarly, the receive control element mayprovide flow control functionality in accordance with a variety ofcommunications protocols, such as, for example, IEEE 802.3xfunctionality. In an exemplary embodiment, system interface 150 mayinclude a transmit data path width of 32 bits and a receive data pathwidth of 64 bits. In the described exemplary embodiment, the systeminterface preferably includes a FIFO 140 that receives data from thereceive data path and forwards data to the transmit data path.

FIG. 4 is a simplified block diagram showing additional details of thereceive function element 200 illustrated in FIG. 3. In an exemplaryembodiment of the present invention, receive function element 200preferably receives 32 bit-wide input data 316 and a standardized clocksignal 314. In an exemplary embodiment of the present invention, thedata 316 and clock signal 314 are received from MCE 101 via the mediaindependent interface 114 (see FIG. 3).

In accordance with an exemplary embodiment, the receive function elementpreferably utilizes dual data rate (DDR) sampling to convert two 32bit-wide serial data streams to a single 64 bit-wide parallel datastream which is output 320 to the receive control element 130 (shown inFIG. 3). In this manner, the receive data path at system interface 150is 64 bits wide while the transmit data path is 32 bits wide.

In one embodiment, the receive function element 200 couples the 32bit-wide input data 316 to two gate elements 302 and 304. In thedescribed exemplary embodiment, one gate element preferably samples theinput data 316 on the rising edge of the clock signal and the other gateelement samples the input data 316 on the negative or falling edge ofthe clock signal. (This will be illustrated in the timing diagrams ofFIGS. 5 and 6.) Consequently, each of the gate elements 302 and 304preferably forward 32 bit-wide serial data streams to master gate 306.

The master gate 306 preferably performs a reverse multiplexing processto convert the multiple input streams of 32 bit-wide serial data 302(a)and 304(a) to 64 bit-wide parallel data in accordance with the risingedge of the clock. In the described exemplary embodiment, rising edgesampling is used for internally processing and outputting 64 bit-widedata.

In operation the de-multiplexed, parallel data 306(a) may be input tologic block 308 which inspects inter-packet gaps (IPGs) of the paralleldata stream and performs preamble insertions and data alignment. Inaddition, in an exemplary embodiment the logic block 308 preferablyanalyzes the parallel data 306(a) and performs statistics generation.

In an exemplary embodiment of the present invention logic block 308forwards a receive FIFO handshake signal 314 to an external FIFO element140 within the system interface (see FIG. 3). In an exemplaryembodiment, the logic block 308 indirectly forwards the receive FIFOhandshake signal 314 such that the FIFO handshake signal 314functionally flows through the receive control element 130 (see FIG. 3)to the external FIFO. The receive control element 130 preferablymonitors the handshake signals as they are going through. After a FIFOhandshake signal is sent, logic block 308 outputs the 64 bit-wide data320 to the external FIFO. In addition, in the described exemplaryembodiment, a cyclic redundancy check element 310 performs a cyclicredundancy check on the current output data and a comparator 312compares the current redundancy check with previous cyclic redundancycheck data. The statistics generated by the logic block and the resultof the CRC compare may then be output 322 for use by other elementsoutside the MAC.

In the described exemplary embodiment, the remaining operations in thereceive pipeline may also use the rising edge of the clock signal 314 onan internal 64 bit pipeline bus. This eliminates the requirement forrising edge and falling edge processing solutions that are difficult torealize due to asymmetries in most clock signals.

FIG. 5 is a wave diagram of an exemplary clock signal 314. It can beseen that the clock signal 314, includes falling and rising edges. Inaccordance with an exemplary embodiment, a first gate element,designated G1, samples consecutive ones of instances of data having afirst width at consecutive rising edges (402, 406, 410, etc.) of theclock. Further, a second gate element, designated G2, samplesconsecutive ones of instances of data having the first width atconsecutive falling edges (404, 408, 412, etc.) of the clock. Datahaving the second, greater width is then processed at the second risingedges 414, 416 of the clock 314.

FIG. 6 graphically illustrates the timing of an exemplary asymmetricdata path. In accordance with an exemplary embodiment of the presentinvention, input data 502 is represented by data bits D1, D2, D3, etc.and includes 32 data bits in a preferred embodiment. The wave/timingdiagram in FIG. 6 shows the timing perspective of how 32 bit-wide inputdata 502 is converted to 64 bit-wide output data 512. In accordance withan exemplary embodiment of the present invention a first gate element302 samples the input data 316 (502) on the “rising” edge of the clocksignal 314 (506). In addition, a second gate element 304 samples theinput data 316 (502) on the “falling” edge of the clock signal 314(508). In the described exemplary embodiment, the master gate 306 (510)converts the two 32 bit-wide data streams 506 and 508 to a 64 bit wideparallel data stream using a subsequent rising edge of the clock signal504. In addition, the 64 bit-wide output data with CRC appended is alsoillustrated.

FIG. 7 is a flow diagram illustrating an exemplary method formanipulating data according to the present invention. Like elements inthe flow diagram of FIG. 7 (MCE 101, master gate element 306, logicblock 308, and receive function element 200, for example) represent likeelements in the preceding figures.

In accordance with an exemplary embodiment, input data 601 includes 32bits of data, 2 bits of management information and 4 control bits. Inthe described exemplary embodiment the MII interface forwards the inputdata to the management control element (MCE). The MCE preferably stripsthe two bits of management information from the input data 603 andforwards the input data 607, comprising the 32 data bits and 4 controlbits to the receive function element 200.

Within the receive function element 200, the input data 607 is sampledin accordance with the rising and falling edges of a clock signal 609 toproduce two data outputs 613, each being 32 bit-wide data. The two 32bit wide serial data streams may then be parallelized in accordance withthe rising edge of the clock 615 to produce 64 bit wide parallel data617. The parallel data may then be processed to generate statistics 619.For example, in an exemplary embodiment, a logic block may inspect theinter-packet gap (IPG) intervals, perform preamble insertions, dataalignment and statistics generation. Before the data is output to thesystem interface, a receive FIFO handshake signal from the receivefunction element 200 is sent to an external FIFO 621.

In accordance with an exemplary embodiment, the 64 bit-wide data isoutput 645, and a cyclic redundancy check (CRC) 635 is performed on thecurrent output data. In accordance with an exemplary embodiment, thereceive function element may check for error in the current CRC bycomparing the CRC data for the current output to stored (old) CRC data.In operation if errors are found 639, the CRC element recalculates thedata 641 and resends the new CRC data 643 for another comparison 635with the old CRC data before outputting the CRC data 637 to receivestatistics. In this manner, data output 645 having a 64 bit-wide datapath, is output from receive function element 200.

It will be appreciated by those of ordinary skill in the art that theinvention can be embodied in other specific forms without departing fromthe spirit or essential character hereof. For example, the presentinvention is not limited to asymmetric data paths wherein the transmitclock is of a sufficient speed to maintain the desired data throughput.Rather, the present invention may be utilized to increase the datathroughput in both the transmit and receive data paths or in thetransmit data path alone. The present description is thereforeconsidered in all respects to be illustrative and not restrictive. Thescope of the invention is indicated by the appended claims, and allchanges that come within the meaning and range of equivalents thereofare intended to be embraced therein.

1. A method for maintaining throughput in a data element, comprising thesteps of: receiving at a first element a clock and a first plurality ofinstances of data having a first bit-width as an input; transmitting theclock and first plurality of instances of data having the first width toa second element, wherein the second element represents a firstcomponent of a media access controller; operating on the first pluralityof instances of data having the first width to produce a secondplurality of instances of data having a second width; transmitting theclock and second plurality of instances of data having the second widthto a third element, wherein the third element represents a secondcomponent of the media access controller; operating on the secondplurality of instances of data having the second width to produce athird plurality of instances of data having a third width; transmittingthe third plurality of instances of data having the third width to afourth element, wherein the fourth element represents a third componentof the media access controller; and operating on the third plurality ofinstances of data having the third width to produce a fourth pluralityof instances of data having a fourth width.
 2. The method according toclaim 1, wherein the first width is
 32. 3. The method according to claim1, wherein the second width is
 32. 4. The method according to claim 1,wherein the third width is
 64. 5. The method according to claim 1,wherein the fourth width is
 64. 6. The method according to claim 1,wherein the third and fourth widths are equal.
 7. The method accordingto claim 1, further comprising the steps of: receiving the fourthplurality of instances of data having the fourth width by a fifthelement; and transmitting a fifth plurality of instances of data havinga fifth width which is half of the fourth width.
 8. The method accordingto claim 1, wherein the first element if a physical layer device.
 9. Themethod according to claim 1, wherein the second element is a managementcontrol element.
 10. The method according to claim 1, wherein the thirdelement is a receive function element.
 11. The method according to claim7, wherein the fourth element is a receive control element.
 12. Themethod according to claim 7, wherein the fifth element is a systeminterface.